The trigger executable cannot find its data directory when built from a tarball or source control checkout using the standard build commands - ./configure; jam. The executable either has to be moved to the data directory or the datadir options specified to configure. When trigger starts it should look in a few places to find the data directory and use the first valid directory found from then on. The search directories are relative to either the current directory (the directory that the executable is in - $DIR) or the configured data directory ($DATADIR). The search directories could be, in order:
The test for a valid data directory could be the presence of a well known file, perhaps data/textures/splash/splash.jpg. The trigger.config.defs file is not suitable for the test as Debian installs that file to /etc not the data directory.